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                城市改建                </h1>
                <p>时间限制：15s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：256MB</p>			</div>
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                                <h3>题目描述</h3><p><div id="psrc" style="margin-top: 20px; display: none">
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<p><span style="font-size: medium">　　cs城由n座美丽的小镇组成，小镇之间通过n-1条公路连接，任意两个小镇都能互达。尽管如此，居民还是会向他们的负责人yy抱怨：两座小镇之间的距离(经过的公路数)太远了！yy体恤民情，打算重建城市。yy认为，n-1条公路足矣，丝毫没有浪费，他决定依旧保持这个结构。并且，yy并不打算大兴土木，因此他只会拆除一条公路再新建一条公路。<br />
　　作为yy的助理，你需要帮他计算出重建城市后最远的两座小镇距离最近是多少(若存在两个小镇不能互达，则距离为无穷远)，并给出任意一组合法方案。<br />
</span></p></p><hr/><h3>输入格式</h3><p><div id="pcont1" style="margin-top: 20px; display: block">
<div class="pdcont"><span style="font-size: medium">　　输入的第一行包含一个整数n。接下来n-1行，每行两个整数a、b，代表一条公路。<br />
</span></div>
</div></p><hr/><h3>输出格式</h3><p><div class="pdcont"><span style="font-size: medium">　　输出3行。第一行包含一个整数，表示重建后最远的两座小镇的最近距离。第二行包含两个整数，代表拆除的公路。第三行包含两个整数，代表新建的公路。<br />
</span></div></p><hr/><h3>样例输入</h3><pre>4
1 2
2 3
3 4

样例输出
2
3 4
4 2</pre><hr/><h3>样例输出</h3><pre>数据规模和约定
　　20%的数据满足：n≤30
　　60%的数据满足：n≤3000
　　100%的数据满足：1≤n≤300000、1≤a、b≤n 保证输入数据合法
　　Note：如果输出第一行正确，后两行有误或缺失，你可以得到该测试点40%的分数
</pre><hr/><h3>提示</h3><p><p>如果有人愿意写special judge程序，请留言给lavendir</p></p><hr/><h3>题目来源</h3><p>没有写明来源</p>
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